1. Field of the Invention
The present invention relates to a thermal image forming apparatus including a thermal printhead to form an image on a sheet of paper.
2. Description of the Related Art
FIG. 1 illustrates a part of a conventional thermal image forming apparatus 10.
Referring to FIG. 1, the thermal image forming apparatus 10 includes a thermal printhead 12 that applies heat to a sheet of paper P while contacting a platen roller 11 and forming a printing nip between the thermal printhead 12 and the platen roller 11. A conveying unit 16 conveys the paper P between the platen roller 11 and the thermal printhead 12. The conveying unit 16 includes two rollers that are rotatably engaged with each other. The thermal printhead includes a plurality of heating elements arranged along an area forming the printing nip. An image is formed on the paper P by the heating elements that are selectively heated by a driving integrated circuit 13 while the paper P passes through the printing nip between the platen roller 11 and the thermal printhead 12. The driving integrated circuit 13 drives the heating elements, and consequently a great amount of heat is generated in the driving integrated circuit 13. Because the driving integrated circuit 13 is disposed toward the paper P supplied between the platen roller 11 and the thermal printhead 12, the heat generated in the driving integrated circuit 13 may be unnecessarily transferred to the paper P through a molding portion 14. When the paper P is not general paper but thermal paper, image deterioration may occur such as vertical bending in which lines are formed on the paper P along the conveying direction of the paper P. To prevent this problem, a cover member 15 is installed to cover the driving integrated circuit 13. The cover member 15 prevents the driving integrated circuit 13 from contacting the paper P and interrupts the heat transfer from the driving integrated circuit 13 to the paper P.
However, in the conventional thermal image forming apparatus, when the paper P is supplied between the platen roller 11 and the thermal printhead 12, which are separated from each other before an image is printed, the leading edge of the paper P can bump against a portion where the cover member 15 and the thermal printhead 12 are connected to each other. Thus, paper conveyance is interrupted, which can cause a paper jam. As illustrated in FIG. 1, the paper jam can occur in a structure in which a conveyance position ‘A’ of the paper P passing the conveying unit 16 is not horizontal to a position ‘B’ of the printing nip formed between the platen roller 11 and the thermal printhead 12, that is, the paper P passing the conveying unit 16 is not horizontally conveyed to the printing nip.
Accordingly, a need exists for a thermal image forming apparatus having improved paper conveyance between a thermal printhead and a platen roller.